code: def test_gridsearch_multi(self):
      dummy_series = st(length=40, value_y_offset=10).stack(
          lt(length=40, end_value=20)
      )
      tcn_params = {
          "input_chunk_length": [12],
          "output_chunk_length": [3],
          "n_epochs": [1],
          "batch_size": [1],
          "kernel_size": [2, 3, 4],
          "pl_trainer_kwargs": [tfm_kwargs["pl_trainer_kwargs"]],
      }
      TCNModel.gridsearch(
          tcn_params, dummy_series, forecast_horizon=3, metric=mape
      )
  
imports: import random
  from itertools import product
  import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.datasets import AirPassengersDataset, MonthlyMilkDataset
  from darts.logging import get_logger
  from darts.metrics import mape, r2_score
  from darts.models import ARIMA, FFT, ExponentialSmoothing, NaiveDrift, NaiveSeasonal, Theta
  from darts.tests.conftest import tfm_kwargs
  from darts.utils.timeseries_generation import gaussian_timeseries
  from darts.utils.timeseries_generation import linear_timeseries
  from darts.utils.timeseries_generation import random_walk_timeseries
  from darts.utils.timeseries_generation import sine_timeseries
label_desc: Use image node_id 11 for calling the TestBacktesting obj's underlying member method code with example usage: obj.test_gridsearch_multi() without return types